1. Field of the Invention
This invention relates to an exhaust converter structured with a catalyst carrier wrapped with a supporting mat and a casing in which the catalyst carrier is incorporated and, more particularly, to an exhaust converter so constituted to recover positional shifts of the supporting mat when the supporting mat is positionally shifted.
2. Description of Related Art
Exhaust converters have a function to convert harmful gases such as hydrocarbon or carbon monoxide contained in exhaust gas of engines to stable compounds such as steam or carbon gas and to discharge the converted gases to the open air.
Such an exhaust converter, as shown in FIG. 8, holds a catalyst containing noble metals for purifying exhaust gas with a carrier 51 made of a ceramic having a honeycomb structure. A supporting mat 52 made of a heat insulator having an elasticity is wrapped over the carrier 51. A cylindrical shaped metal plate 53 is wrapped on an outer periphery of the supporting mat 52 and fastened tightly to support the carrier 51 in operating compression force to the supporting mat 52, and subsequently, the cylindrical shaped metal plate 53 is welded to form a casing, thereby maintaining a high gas-sealing property.
With the above exhaust converter, when a cylindrical shaped metal plate 53 is formed having a constant radius of curvature, spaces between the carrier and the metal plate become different between an overlapped portion 54 and other portions, so that uneven load is exerted to the carrier. The carrier therefore may be broken by exertion of uneven force.
To solve the above problem, a method for manufacturing a catalyst converter disclosed in Japanese Unexamined Patent Publication (KOKAI) Heisei No. 10-121,953 has been proposed. In this art, the converter includes a pipe-shaped metal shell having a constant radius of curvature, and an overlapped portion is structured to have the same radius of curvature as the outer periphery of the shell. With this art, where the shell is wrapped over the outer periphery of the supporting mat, no spot load occurs along the overlapped portion at the shell.
The supporting mat 52 wrapped on the carrier is, as shown in FIG. 9, formed with projections 52a formed at each end in a longitudinal direction to face with one another, and the mat 52 has a length that each end does not overlap with each other when the mat is wrapped on the carrier.
However, when the metal plate is wrapped and fastened on the outer periphery of the supporting mat wrapped on the carrier, the metal plate moves in a circumferential direction, thereby reducing the diameter of the plate. According to the movement of the metal plate, the supporting mat is shifted to exist unevenly on a side and gathers at the overlapped portion of the metal plate. Consequently, a concentrated load is exerted to a position corresponding to the overlapped portion of the metal plate of the carrier, thereby rendering possibly the carrier broken down.
Such a problem occurs regardless whether the space between the catalyst converter and the cylindrical shaped metal plate is constant or not, and occurs according to the movement of the metal plate in the circumferential direction which occurs at a time that the metal plate is tightly fastened, so that the art disclosed in the above Publication will not solve the problem.
It is an object of the invention to provide an exhaust converter for preventing the carrier from broken down upon preventing the carrier from receiving a concentrated load by recovering, with recovering means, positional shifts of the supporting mat which occur when the metal plate wrapped over the outer periphery of the supporting mat is fastened tightly.
An exhaust converter according to the invention includes a catalyst carrier made of a ceramic material, a supporting mat wrapped on an outer periphery of the catalyst carrier, a casing formed in a cylindrical shape incorporating therein the catalyst carrier wrapped with the supporting mat, and recovering means formed at either or both of the supporting mat and the casing for recovering positional shifts of the supporting mat.
The above exhaust converter can recover positional shifts occurring according to fastening of the casing since the above exhaust converter is formed with the recovering means formed at the supporting mat or at the casing or at both of the supporting mat or the casing for recovering positional shifts of the supporting mat. Therefore, the positional shifts do not operate to the catalyst carrier as to give concentrated loads to the carrier, so that the catalyst carrier will never be broken down.
With the above exhaust converter, it is preferable to provide a friction reducing means placed between an inner surface of the casing and the supporting mat for reducing friction between the inner surface and the supporting mat. By providing the friction reducing means between the inner surface of the casing and the supporting mat, the movement of the supporting mat in association with the casing when the casing is fastened tightly can be reduced effectively. Therefore, the shifts occurring at the supporting mat can be reduced.